[Matt Vogt]

I ordered a 14.8V 2800mAH Li-ion battery pack for my current project, ignorantly assuming that the cells were the same size as Nicad and the like. Doh!
When I received them and found that the pack is too large for my purposes, I planned to separate it into two packs in series. However, I know Li-Ion is a different breed of battery. Is this plausible to separate them?

Thanks,

Matt

 

[TonyWalsham]

Not if they have built in electronics to protect them.
It is critical that you do NOT TOUCH the electronics and be extremely careful not to puncture or damage the cells in any way.

I know of a serious fire that occurred very recently when a modeller accidentally drilled into a Lithium pack. It erupted like a volcano and it took 5 minutes to put out the fire. All that was left were the wheels, motor and part of the frame.
An expensive lesson.

 

[Greg Elmassian]

Not to argue with Tony, but you could separate them, if you can determine how they are connected, and there is a reasonable way to do this.

First, obviously all the cells will be in series, so you need to maintain that. Many packs have "per cell" monitoring, which means the internal electronics connects to EVERY cell inside. That will make things much more tricky.

Also, if you need to lengthen the "Wires" (often stainless steel straps spot welded to the cells), you cannot get heat on the cells, like you could get away with on a nicad.

Bottom line, VERY careful repositioning is fine, but you cannot go south of the electronics.

Of course, the pack will be non-returnable if you do anything physical to it. You can cut off the thin outer shrink wrapper to see if you want to try, but then you are in "non-returnable" land.

Regards, Greg

 

[Matt Vogt]

Thank you gents, for taking the time to respond.
I am thinking that perhaps my first experience with Li-Ion batteries should not involve disassembly of a pack. Theerefore, I have ordered two 7.4V packs to straddle the interior. I haven't decided whether or not it is worth losing the shipping to return the first pack, or save it for my next battery project. I think I remember reading that these have a long shelf life. Is that true?

Thanks again,

Matt

 

[paintjockey]

They are supposed to have a long shelf life, I've only had mine for a year so I can't speak from experience.

 

[Greg Elmassian]

recharge it occasionally, that will be best....

Regards, Greg

 

[Dean Whipple]

They have a long shelf life.....I bought a couple of batteries charged them and was not able do do anything with them....2 1/2 years later they still had a full charge, I put them in a couple engines....I've been using it for almost a year now, they work great.

 

[Greg Elmassian]

not all li-ion batteries will hold a charge 2.5 years... try that with your cell phone... best to check them every once in a while, unless you want to take the chance to be the guy with one burning up on him, because one cell reversed ... not worth the risk in my opinion.

Once someone has had a battery fire, they usually get a bit more conservative.

Regards, Greg

 

[Mike Reilley]

Posted By Greg Elmassian on 03/04/2009 11:20 PM
...best to check them every once in a while...
Regards, Greg


Once they're in the engine....how does one do this without removing the pack and taking the pack apart?

 

[Dan Pierce]

I believe most cell phones are never fully off and that is why the batteries discharge. They are on for remote access by those that claim they do not watch us.

Many electronic items built now do not have full off capabilities unless you remove the batteries or unplug them.

Cars have clocks, remote control sensors, alarm systems, radios that need battery backup. Batteries go dead in a week at the airport on some models (my grand Prix was like that).

If a unit has a remote control for power turn on, it is never fully off!!!

 

[Greg Elmassian]

Mike, are you setting me up? ha ha!

Yeah, one cell going bad in a pack that does not have per-cell connections can only be determined by trying to charge the pack and seeing the terminal voltage (or the pack melting down, no kidding).

Depends on how "Bad" the cell goes.

All the more reason for regular maintenance of a battery pack.

Dan, I was not specific enough. Charge your phone. Take the pack out. See if it holds a charge for 2.5 years. It will not. Not all rechargeable lithium packs are DESIGNED for long shelf life. Cell phones DON'T need long shelf life like a flashlight sitting in your trunk does. Everything in battery design is a tradeoff with something else. (Sorry I was not clear in my example).

Regards, Greg

 

[Road Foreman]

Boy are Li-Ion battery's getting big!! Had some electricans up-grade my house wiring & they were using 24 volt Milwaukee drills & saws.. I said that was the biggest I had seen.. There comment was these are small, new 1's are 36 & 48 volts.. There batterys had test buttoms so you could see how much battery you had left..

BulletBob

 

[K27_463]

What Greg meant to say was that if storing Lithium for long periods of nion use, it is best to simply put them on a maintenance charge every three months or os. This does not mean you need to full charge them. One of the big advantages of LI is thlack of need to full cycle them. So, simply avoiding a complete discharge in storage is enough. Charge them for an hour or so every few weeks or months and you will be fine for a long time. When ready to run, put them on your charger and let it shut off to peak them up, that is all. The other point abpout LI is that most modern smart chargers now are peaking them at about 95% of capacity. The last few percent are not critical and avoid the excessive heating that comres with forcing the last bit pf power in. i had one charger that if 6 hours achieved 95%, for example then the last 5% was another 6 hours. It simply went into a very low level trickle charge after the cell was essentially full. Lithium will degrade in storage less than either nicad or nimh , as long as they are moderatley maintained with at least some charge in the pack.
jonathan/EMW

 

[Mike Reilley]

Some good advice....

http://www.rcgroups.com/forums/showthread.php?t=209187

 

[billsharron]

I have had no problems soldering on Li-IOn batteries at all. I make my own packs using 3.7 volt 2600 Mah batteries with built in PCB protection. I use a 250 watt iron, p[lenty of flux and get in and out very quickly. I can make a 14.8 volt pack for less then $30. When using a smart charger the meter shows 15.6 volts at full charge. I get them at all-battery.com very fast service and excellent quality.

 

[Greg Elmassian]

Bill, I too will solder on li-ion batteries, fast and with a hot iron.

But, I would caution people who are not pretty expert at soldering to NOT DO THIS!

Yours and my idea of "quickly" might not be the same as someone less experienced... and this could easily start a fire.

My advice is to have an expert solderer do this, or go to the local battery supply place and have them spot weld the straps to make up a pack. If you have batteries with "tabs" on them already, then this is not an issue, although be careful anyway!

Regards, Greg

 

[izzy0855]

Hello Matt,

No, you can not separate a Lithium-Ion battery-pack. Every Lithium-Ion battery-pack is manufactured with a PCB Circuit board that controls your batteries charge / discharge current to it's designed voltage (ie: 7.4V, 11.1V, 14.8V, or 18.5V). You could send us your battery-pack, we can remove one cell and remanufactured it into a 11.1V pack with a new PCB board and send it back to you, but; you would need a 11.1V Lithium-Ion charging unit. Check out our website at www.cordlessrenovations.com and click up chargers to our new CR-1 Smart Charger. Then give me a call and I'll help you out.

Rick Isard, owner
Cordless Renovations

 

[Greg Elmassian]

I think "separate" meant re-arrange the cells physically, not electrically. If there is confusion about this term "separate" maybe Matt could speak up.

Regards, Greg

 

[Matt Vogt]

Hello, Rick, and welcome to MLS! I appreciate your taking the time to post. I have looked over your site, and see that you are no stranger to large scale trains - nice to know.

Sorry for the confusion, but Greg is correct. When I spoke of separating the batteries, I did mean physically into two 7.4V packs, which I decided to order instead, and received yesterday. I haven't really decided whether to keep my originally ordered pack for a future project, or return it, but I will keep you in mind in the future either way.




Take care,
Matt

 

[Torby]

Pleased to meet you, Rick. Nice to have a battery expert around.